The present invention also relates to making a compressor, in particular of the axial type, more particularly a compressor operating at low pressure, but also a compressor operating at high pressure, and including a casing as mentioned above.
The present invention also relates to a turbomachine, in particular a turbojet, including such a casing or such a compressor.
Compressors of this type, as used in particular in turbojets, are constituted by a rotor comprising either a succession of separate disks stacked one after another, or else a single drum for receiving the series of blades of the various stages.
Conventionally, the rotor includes slots made by machining so as to form a gap between two adjacent stages, which gap receives the vanes of stator stages that are secured to a stationary portion presenting a casing.
The casing forms a segment of the radially outermost zone of the flow section in which air passes through the turbomachine.
It is usual for the moving blades to be secured individually to the drum via housings that are distributed regularly and that are present in number equal to the number of blades, each housing being of a shape that is designed to co-operate with a blade root of complementary shape, thereby ensuring that each blade is held radially, e.g. by a fastening of the dovetail type. Usually, the blade roots are held against moving in translation, in particular axial translation relative to their respective housings, by separate means for each blade, e.g. by a system making use of a ball, a pin, a staple, a plate, a spacer, etc.
While a turbojet (especially a modern civil aeroengine) is in operation, and given the temperatures and pressures reached by the hot air, it is necessary to provide a regulation function in the event of pumping.
It should be recalled that pumping is a phenomenon that it is desirable to avoid within an engine since it gives rise to sudden oscillations in air pressure and air flow rate, thereby subjecting the blades to high levels of mechanical stress that can weaken them or even break them. This phenomenon can be initiated by pressure oscillations at the outer end of the blade, with interaction between the boundary layer at the tip of the blade and the boundary layer at the casing being strong.
Likewise, rotating separation is a phenomenon that occurs when certain throttling (operating point) and speed of rotation conditions are combined. In particular, this phenomenon is triggered when the profile is put into a so-called “positive” incidence, giving rise to a non-steady phenomenon that leads to separation occurring locally at one blade, which separation then propagates from one blade to another during a revolution.
This phenomenon is particularly damaging:                Blades become polluted by generalized separation which will lead to pumping; and        there is a risk of aeroelastic excitation of the blades involved.        
At present, this function of regulating pumping is performed by various types of solution, including discharge valves that enable the boundary layer to be sucked out, or casing treatments that cover the entire annular surface of the annulus facing the moving blade wheel(s) to be treated.
This casing treatment solution has given rise to numerous different embodiments. In particular, in document EP 0 688 400 proposals are made for an annular cavity communicating with the flow path via slots defined by an annular grid of sloping ribs. In document U.S. Pat. No. 6,514,039, the technique is similar and in addition, material treatment, such as laser shock peening, is performed on the bar forming the intermediate part for forming the grid, said treatment serving to make it better at withstanding failure by fatigue.